The influence of the oxygen concentration, the oxidation-reduction potential and the pH of the flotation slurry on the recovery and on the quality and selectivity of individual metals recovered from ores by flotation has often been described in the prior art.
In "The Role of Oxygen in Sulfide Ore Flotation", Panaiotov, V.; Semkov, N.; Arnaudov, R.; Mirchev, V. (Bulg.) Obogashch. Rud (Leningrad) 1986 (4) 16-18, (Russ), the increase of the oxygen concentration is described as having different influences on the recovery of different metals. It is also concluded that the control of the oxidation-reduction potential can be used to optimize the selective recovery of minerals from complex ores by flotation.
In "Algorithms of the Conditioning of a Slurry of Uniform Copper-Nickel Sulfide Ores" K. G. Bakinov, Yu V. Shtabov (USSR) Teor. Osn. Kontrol Protsessov of Flotatsli 1980, 198 to 204, (Russ), the improvement of the flotation of polymetallic sulfide ores by an optimizing of the oxidation-reduction potential is described.
In "Evaluation of Processes occurring in the Flotation of Pulp", S. B. Leonov, O. N. Bel'kova, Veshchestv. Sostav Obogatimost Miner. Syr'ya 1978, 74-8, (Russ), effects are described which depend, inter alia, on the oxidation-reduction potentials in the aqueous phase and in sulfide minerals in the flotation pulp and on the hydrophobizing of the sulfide ores. The selective flotation of lead sulfide, zinc sulfide, and copper sulfide is also described.
Published Soviet Patent Application SU-O 1,066,657 discloses a process in which the oxidation-reduction potential is achieved by a change of the degree of the aeration with air, namely, by a change of the rate at which air is introduced into the pulp. The time of aeration and the time in which the rate of change of the oxidation-reduction potentials are measured in minutes throughout the measured aerating time.
XVIth International Mineral Processing Congress, edited by E. Forssberg, Elsevier Science Publishers B. V., Amsterdam 1988 "Selective Flotation of Sulfidic Complex Ores With Special Reference to the Interaction of Specific Surface, Redox Potential and Oxygen Content" A. N. Beysavi, L. P. Kitschen, pages 565 to 578, discloses the selective flotation of copper from copper-lead-zinc ores, which are particularly rich in pyrites. It has been shown that an optimum adjustment of the oxidation-reduction potential before the first flotation stage, namely the flotation of copper, will result in a remarkable improvement of the selectivity. It is also apparent from that publication that the oxidation-reduction potential depends on the particle size of the ground ore, on the pH and on the regulators. The ore was finely ground and was then slurried in water. The resulting suspension was filtered and the filter cake was intensely washed with fresh water to remove the so-called toxic components, such as S.sup.2-, S.sub.2 O.sub.3.sup.2-, SO.sub.3.sup.2- and SO.sub.4.sup.2-.
The solids were reslurried and the slurry was first aerated with air to adjust a certain oxidation-reduction potential and was then conditioned with SO.sub.2 and thereafter with CaO and finally with collecting and frothing agents.
Throughout the process the oxidation-reduction potential and the oxygen content and the pH values were measured. The oxidation-reduction potential, which was selected for the flotation of Cu, was adjusted by control of the rate at which oxygen was supplied by the aeration before the conditioning with SO.sub.2.
The investigations have revealed the strong dependence of the flotation of Cu on the oxidation-reduction potential. The experiments were carried out at oxidation-reduction potentials from -260 mV to +183 mV. It has been found that, e.g., at -260 mV the froth consists almost exclusively of purities and only 1.3% of the solids in the froth consist of copper. At oxidation-reduction potentials from 171 mV to 183 mV it could be shown that galena begins to enter the froth so that 14 to 41% of the lead contained in the ore was already present in the froth.
It could also be shown that for the investigated ores there is an optimum range for the oxidation-reduction potential in which a high percentage of the copper is recovered with a high selectivity of Cu in the flotation of Cu.
That publication teaches that the recovery of copper and the selectivity of the separation of copper cannot be increased further. The other publications discussed hereinbefore also fail to suggest how the recovery and the selectivity can be improved further.